A need exists for rapid and accurate measurement of the core temperature of humans as well as animals, particularly, but not limited to, domestic food animals such as cattle, sheep, and goats, as well as horses. Core temperature, the internal body temperature, or more precisely the temperature of the blood as it flows in or near the pulmonary artery near the heart, has been difficult to measure accurately without physical contact with the sensitive interior of the body. Such measurements require a surgically invasive insertion of a temperature probe and this is rarely justified except in critical surgery. In practice, core temperature is not really measured but is approximated with rectal, oral and ear thermometers and others. A better, more accurate and more rapid measurement of actual core temperature is needed for use at home, in the offices, in animal barns, hospitals, clinics and many other places and situations.
In the United States' cattle industry, annual mortality of cattle due to disease is estimated to be in the hundreds of millions of dollars. A reliable method of determining the health of a cow or the presence of disease is by assessing the body temperature of the animal. In the case of infections, environmental factors, or toxins, a cow's temperature will elevate. These elevations are diagnostic to veterinarians in the diagnosis of disease and disease conditions in cattle. In the day-to-day production of cattle, the evaluation of the presence of increased body temperature or fever is under utilized due to time constraints and the need to physically restrain the animal. This under utilization of temperature evaluation delays the diagnosis of disease and therefore increases the use of antibiotics and loss of animals.
Traditionally, to obtain temperature measurements, clinical thermometers have been inserted rectally or orally and must remain in position for periods of several minutes to obtain a stable reading. This usually requires restraint of the animal, which is time consuming and labor intensive. Typically, the body temperature of cattle is measured with a clinical mercury Fahrenheit thermometer or with a digital thermometer. A mercury thermometer has a scale ranging from 94 F. to 110 F. and each degree is divided into ⅕ths. The thermometer requires shaking the mercury column into the bulb end. The thermometer is then lubricated or moistened and manually inserted its full length into the rectum. It remains in the rectum for a minimum of 3 minutes to obtain an accurate reading. As most animals object to this procedure, the animal must be physically restrained during this time.
In recent years, temperature sensors of low thermal mass, such as miniature thermocouples or thermistors, have been used with an electronic digital readout to make the more rapid digital thermometers. However, these devices still require oral or rectal insertion and restraint of the animal but the time for accurate measurement is only one minute.
Other approaches to animal temperature measurement are based on sensing the thermal emission energy, the so called black body emission. This energy is emitted as a wide band electromagnetic spectrum by all heated bodies and has a wavelength distribution and intensity in proportion to temperature. This emitted energy is detected by use of a non-contact microwave, millimeter (mm) wave, or infrared (IR) sensors. Thermal emission measurement is rapid, but the accuracy by which the thermal emission is related to temperature is affected by two factors, in addition to instrumental errors, if any. The first factor is how accurately an emitting surface that is accessible for measurement relates to the core temperature. This frequently poses a problem with animals and humans in that skin may not be a true representation of the internal temperature. This is particularly a problem with Infrared (IR), where the depth within a body from which the emission is detected is very shallow and is essentially proportional to the outer temperature of the skin. The second factor, surface emissivity, also affects the amount of thermal emission from a body at a given temperature. This causes temperature measurements, based on thermal emissions, to vary depending on the color and the physical properties of the materials being measured. To attempt to overcome this source of error, some IR thermal emission thermometers use a probe inserted into the ear. However, surface emissivity in the ear can vary due to the amounts and types of debris and these can limit the accuracy. In another variation, an insert is placed in the ear of the animals to provide a constant emissivity target for the IR sensor. The insert must be in the ear for a sufficient time to reach thermal equilibrium prior to measurement, which is undesirable from cost and time considerations.
The possibility of measuring the core temperature of cattle by remote (hands-off) sensing has been of great interest over the past 30 years or more. Previous approaches have been based on (1) passive detection of the magnitude of the IR or microwave energy that is emitted in proportion to the temperature and wavelength (in accordance with Planck's law) from most materials including human or animal hide or ear (interior); (2) the use of implants and/or tags which use contact type thermal sensors (thermistors, thermocouples, etc.) and usually a wireless means of reading out the data on demand; and (3) the use of ingested temperature sensing capsules which contain a temperature sensor and a radio frequency (VHF or UHF) transmitter or transponder to communicate the temperature data from the interior of the animal to an outside read out unit. None of these previous devices or approaches is completely satisfactory due to cost, poor accuracy, practical application limitations, or other reasons.
Existing passive IR emission thermometers are of limited accuracy (+/−1 degree or worse). These methods are based on sensing surface (skin or hide) temperature and do not have sufficient accuracy nor repeatable for direct measurement of animal body temperature. Skin temperature is not always an accurate indication of the internal temperature of the animal. Also, the emissivity of hair-covered skin is variable and, with IR, will not provide accurate skin temperature nor core temperature indications.